The biological cost of consciousness

Some philosophers maintain that consciousness as subjective experience has no biological function. However, conscious brain events seem very different from unconscious ones. The cortex and thalamus support the reportable qualitative contents of consciousness. Subcortical structures like the cerebellum do not. Likewise, attended sensory stimuli are typically reportable as conscious, while memories of those stimuli are not so reportable until they are specifically recalled. 

Reports of conscious experiences in normal humans always involve subjectivity and an implicit observing ego. Unconscious brain events are not reportable, even under optimal conditions of report. While there are claimed exceptions to these points, they are rare or poorly validated. 

Normal consciousness also implies high availability (rapid conscious access) of the questions routinely asked of neurological patients in the Mental Status Examination, such as common sense features of personal identity, time, place, and social context. Along with “current concerns,” recent conscious contents, and the like, these contents correspond to high frequency items in working memory. While working memory contents are not immediately conscious, they can be rapidly re-called to consciousness. 

The anatomy and physiology of reportable conscious sensorimotor contents are ultraconserved over perhaps 200 million years of mammalian evolution. By comparison, full-fledged language is thought to arise some 100,000 years ago in homo sapiens, while writing, which enables accel-erated cultural development, dates between 2.5 and 6 millennia. Contrary to some claims, therefore, conscious waking precedes language by hundreds of millions of years. 

Like other major adaptations, conscious and unconscious brain events have distinctive biological pros and cons. These involve information processing efficiency, metabolic costs and benefits, and behavioral pros and cons. The well known momentary limited capacity of conscious contents is an example of an information processing cost, while the very large and energy-hungry corticothalamic system makes costly metabolic demands. 

After a century of scientific neglect, fundamental concepts like “conscious,” “unconscious,” “voluntary” and “non-voluntary” are still vitally important, because they refer to major biopsychological phenomena that otherwise are difficult to discuss. 
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